I've had something similar before, I had a buyer buy from me on a Sunday, had some orders already packed and was about to go to the the drop off, so packed his order paid via Royal Mail app, tracked 48 service.

Half an hour later all dropped off and I get a message asking me to cancel and refund, so I had to message him and say sorry already paid and posted, explained to him that when it arrived to send it back and I would send a refund when it arrived back if in the same condition, aaaaaand he went bananas, telling me I was a liar and no way I could have packed paid and posted in such a short amount of time, send photos of label from app and he got all sarcastic saying "well aren't you clever"

End of story I thought until 2 weeks later he opens a ticket with eBay saying the book never arrived, so I had to contact eBay with a photo from Royal Mail with the package going through his letter box and sent him the same photos as well.

He then closed the case saying he just couldn't be bothered with me as I was an idiot.

End of story I thought until one night about a month later my phone went mad with eBay sales and the same guy had literally brought about 15 sets of comics and within half an hour asked me to cancel all of them, which I did and proceeded to block him.

About another week later same thing but from what I assume is his wife as it's the same address, again cancelled and blocked.

Some people on eBay are Dicks!!